The removal of impurities from water and other liquids has been a longstanding problem in the art and, more recently, as our society has become more sophisticated and complex this problem of treating water and other liquids to remove impurities therefrom has become even more serious. This particularly is true in the area of removing undesirable anion, cations, and organic contaminants from liquids.
In recent years, it has been the rule to remove undesirable substances from water by contacting the water with an ion-exchange resin or an adsorbent resin. Ion-exchange materials are either cation exchangers or anion exchangers. Exchangers of the cation type normally have exchangeable hydrogen ions and are utilized to remove the cations contained in a liquid by exchanging the hydrogen ions for the cations. When the cation exchanger is exhausted it is regenerated by passing an acid therethrough such as sulfuric or hydrochloric acid.
An anion exchanger contains easily exchangeable anions such as as ammonia or hydroxyl ions and is utilized to remove undesirable anions from the liquid to be treated.
When complete deionization is required the liquid (e.g. water) to be deionized can either be passed through a cation exchange resin and then an anion exchange resin or, in the alternative, the liquid to be deionized may be passed through a so-called mixed bed of ion exchange resins which includes both cation and anion exchange resins. The mixed bed is normally a homogeneous admixture of cation and anion exchange resins.
In addition to the foregoing types of deionization, one may also utilize a so-called stratified bed, which can be either a cation exchange resin bed or an anion exchange resin bed. If they are used in conjunction with each other to provide complete deionization, the liquid to be deionized is passed first through the cation exchange stratified bed and then through the anion exchange stratified bed.
In an anion exchange stratified bed it is normal to have down flow service (i.e. the water to be treated enters the top of the bed and exits from the bottom) with the weak base anion exchange resin being on top and the strong base anion exchange resin being on the bottom so that the water has to contact the weak base anion exchange resin first. The weak base anion exchange resin removes the strong acid ions such as the chloride ion and sulfate ion whereas the strong base anion exchange resin removes silica and carbon dioxide as well as any residual strong acid ions.
When the anion exchange resin is exhausted it is normally regenerated by utilizing alkaline solutions such as sodium hydroxide. If sodium hydroxide is utilized as the regenerating solution or liquid the anion exchange resin will contain easily exchangeable hydroxyl ions.
Adsorbent resins or polymers are materials which are useful in treating liquids such as water by removing organic contaminants (e.g. phenols) contained therein by a process known as adsorption. When the liquid containing the organic contaminants is passed through the adsorbent material (which is normally in granular or bead form) the organic material is adsorbed through the surface of the resin.
Adsorbent resins may be regenerated, i.e. the adsorbed material may be removed from the adsorbent resin and the resin used again, by a variety of regeneration liquids. For example, various polar organic solvents can be used as regeneration liquids. In order to be satisfactory the regeneration liquid should be a good solvent for the adsorbed material as well as interacting with the surface of the adsorbent resin. In general, methanol is an excellent regeneration liquid.
If potentially ionic materials are being adsorbed then an alkaline liquid (e.g. an aqueous solution of sodium hydroxide) can be used when the adsorbed material is acidic and when the adsorbed material is basic then an aqueous solution of acid may be used. It should be noted that regeneration solutions or liquids for adsorbent resins are known in the art and therefore no detailed exemplification thereof will be given since the present invention is not predicated on the use of these regenerants.
Prior art systems for treating liquids such as water utilizing treating material such as ion exchange resins, although being relatively efficient, do have a number of disadvantages. For example, the life of the ion exchange resins is relatively short and the efficiency of the regenerating solution necessary to regenerate the exhausted ion exchange resins is only 60% to 80% thereby using excess regeneration solution and making the purification system very expensive. Moreover, the resin capacity is not great (particularly after the resins have been in use for any period of time) and the quality of the water is often not good, particularly if the flow rate is sufficiently high to be practical.
From the foregoing it is apparent that it is desideratum in the art to embody a liquid treating system wherein water or other liquids can be purified and treated easily, rapidly and efficiently by maintaining high quality water for extended periods of time and at rapid flow rates and, at the same time, provide long resin life and fast and inexpensive regeneration of the exhausted resins.